[patch] Fix __clear_cache on ARM

[Tim Northover]

> Current gcc's produce an error if __clear_cache is anything but
>
> __clear_cache(char *a, char *b);

Oh good, that makes things a lot simpler.

> The attached patch implements that. I looks like we were just
> implementing a bug of previous gcc versions :-(

It looks reasonable to me. There's no way the same function could work
for both zero and two arguments anyway.

Tim.